Refrigerant recovered from refrigeration systems must be reprocessed with little or no release of the refrigerant to the atmosphere. In systems for purifying and reclaiming of refrigerant, in particular by emptying or renewal of old refrigeration systems, it is relevant to collect the volatile liquid, e.g. R-12, R-22 and R-134A, upon the refrigerant being brought from its gaseous phase to its liquid phase in a condenser, such that the collected refrigerant may be reused.
In principle, the condensate may be filled into a collector tank without the latter having to be vented, because the vapor or gas of the condensate in the upper tank space will maintain its gas pressure also when this space is narrowed by the progressive charging of liquid condensate into the tank. As the condensate rises in the tank the gas will diffuse or condense down into the liquid, such that the gas pressure above the liquid will remain constant when the temperature is constant. Normally, however, there will occur a certain separation of non-condensible gas, mainly of atmospheric air, and as the tank is filled this gas will give rise to increased pressure in the tank concurrently with a further pressure built-up due to the separation of non-condensible gas from the currently introduced condensate.
Non-condensible gas must be separated from the recovered refrigerant as one of the purity requisites of recycled refrigerant. The increased pressure caused by the non-condensible gas also gives rise to some problems, e.g. an increase of the condensation pressure, whereby more energy is needed for the condensation of the volatile liquid and if the collector tank is to be utilized just reasonably effectively, i.e. to be nearly filled for collecting reasonably large portions of the condensate, ready for delivery, then it is in practice imperative to carry out from time to time, a blowing off of the non-condensible gas from the tank.
It is well known that this can be done based on the use of a pressure switch controlled blow-off valve at the top of the tank for automatically initiating blowing off when the pressure in the tank has risen to a predetermined maximum. The blowing off can be interrupted when the pressure has decreased suitably optionally controlled by the hysteresis of the pressure switch. Such a pressure switch is disclosed in U.S. Pat. No. 5,467,608, the disclosure of which is hereby incorporated by reference.
However, the blowing off itself gives rise to problems in that along with the letting out or purging of the non-condensible gases, in the following named air, a certain amount of condensible refrigerant gas will inevitably be expelled. From an environmental point of view, this is very undesirable in the case of a release of considerable amounts of refrigerant gas originating from the refrigerants R-12 and R-22, for example, which have a decomposing effect on the ozone layer around the planet. Such a co-outflow of the condensible gas is particularly noticeable when the temperature is relatively high, because the concentration with the pressure contribution of the condensible gas will then be relatively high in the collector tank.
This circumstance is made even worse by the fact that during the opening time of the blow-off valve the pressure in the collector tank will be reduced such that the condensate will evaporate further, whereby towards the end of the blow-off period there will occur a further increased content of the condensible gas in the purge gas mixture of the blow-off product. Thus, the process for separating of non-condensible gas from the recovered refrigerant must minimize simultaneous release of refrigerant during the venting of non-condensible gas to the atmosphere.
A possible solution to this problem resides in mounting a cooler element in connection with a blow-out pipe from the collector tank, such that the exhausted gas will generally be cooled to the condensation temperature of the condensible gas, whereby the critical fraction of the gas is condensed and falls back into the tank without getting out to the atmosphere. However, experiments have shown that in practice this solution is unrealisticly expensive for it to be reasonably effective, since during the relatively brief blow-out periods a particularly intensive heat exchange with the blow-out gases must take place. There is a need for an improved method and apparatus for recovering/recycling refrigerant wherein the venting of non-condensible gas particularly air, from the collector tank can be carried out while reducing or minimizing the amount of condensible gas that will be expelled to the environment by way of the purge gas.